A collar for use on a water filtration tank adapter. The collar is formed as a ring adapted to thread onto the tank connection end of the adapter and abut the nut portion between the tank connection end and the pipe end of adapter. An o-ring, square in cross-section, is disposed on a top surface of the collar, offset medially towards the center. This top o-ring is adapted to abut the nut portion of the adapter. Another o-ring, square in cross-section, is disposed on the bottom surface, offset medially away from the center. This bottom o-ring is adapted to abut the tank head upon use. Accordingly, a water-tight seal is formed at the tank connection end and tank head, the collar functioning as both a positive stop and as a substitute for pipe tape.